Apparatus and process for producing twist in textile yarns

ABSTRACT

A false twist device comprising an annular rotating friction surface and a rotatable guide extending into the annulus of the friction surface in such a way that the yarn enters and leaves the device on the same side and the contact between the yarn and friction surface takes place outside the annulus.

United States Patent [1 1 111 3,802,175 Doschko Apr. 9, 1974 APPARATUS AND PROCESS FOR [56] References Cited PRODUCING TWIST IN TEXTILE YARNS UNITED STATES PATENTS [75] Inventor: Werner Doschko, Am Leimbach, 3,066,473 12/1962 Maeda 57/77.4 Germany 3,527,043 9/1970 Sabaton 57/77.4 3,643,412 2/1972 Maeda et al... 57/77.4 X [73] Assignee: Imperial Chemical Industri s 3,685,273 8/1972 Neveux 57 157 TS x Limited, London, England 3,724,196 4/1973 Holland et al. 57/774 [22] Filed: Man 1972 Primary Examiner-Donald E. Watkins [21] Appl. No.: 232,375 Attorney, Agent, or Firm-Herbert M. Adrian, Jr.

[30] Foreign Application Priority Data [57] ABSTRACT Mar 8 1971 Great Britain 6270/7 A false twist device comprising an annular rotating friction surface and a rotatable guide extending into [52] U S Cl 57/77 4 57/157 TS the annulus of thefl iction surface in such a way that [51] Int Cl IIIIIIIIIIIIIIIIIIIIIIII oz 1/04 the yarn enters and leaves the device on the same side [58] Fieid 51.6 773 and the contact between the yarn and friction surface takes place outside the annulus.

12 Claims, 4 Drawing Figures PAIENTEUAPR 9 m4 sum 1 0F 2 APPARATUS AND PROCESS FOR PRODUCING TWIST IN TEXTILE YARNS The present invention relates to an apparatus and process for producing twist in textile yarns and is particularly useful in the production of texturised yarns using the false twist principle in which the twist is transmitted to the yarn from a rotating body by friction. The invention also provides the yarn produced thereby. One of the main reasons for inserting twist into a moving yarn is to produce what is known as a texturised yarn. One widely used method for the production of texturised yarns is that of false twisting in which a yarn is twisted, set by heating in its twisted state and subsequently detwisted to give a bulked yarn. In a continuous process the yarn is first passed through a heater and then to a twist device. In this way the twist device imparts a twist to the yarn which runs back into the heater where the twist is set in the yarn. The twist device then has the additional effect of detwisting the yarn when it leaves the device so that the act of detwisting the set twisted yarn produces a bulked yarn.

Various methods are known for producing a twist in a moving yarn. In one of these, yarn is wrapped around a twist pin while passing through a rotating tube, the pin rotates with the tube and is inclined at an angle to the axis of rotation of the tube so that the dynamic equilibrium between the rotating tube and the yarn effects a twist in the yarn. This method is very accurate with respect to the transfer of twist to the yarn, the twist in the yarn being determined by the speed of the twist head. However, with this method only one twist may be inserted for one rotation of the spindle and thus the rate of twist is eliminated when friction alone is used for producing the twist; one method for producing twist by friction is to pass the yarn through a rotating, hollow cylindrical body, the inner surface of which has a friction surface. The yarn contacts the friction surface at an angle to the direction of rotation of the friction surface and with a defined contact pressure so that it is twisted as it moves over the friction surface. Using this principle it is possible to produce larger numbers of yarn twists with one turn of the annular body. This technique has the commercial disadvantage that it is necessary to pass the yarn through the twisting device which leads to problems in threading up and in machinery manufacture and operation where it is desirable to rotate several twist units from a common belt drive so that it is necessary to stop all the units to thread up one.

There are appliances for twisting textile yarns using friction which have a rotationally symmetric annular friction surface which turns on a fixed axis and comes into contact with a tensioned, moving yarn at at least one point in which the yarn approaches and leaves the appliance from the same side. In these devices the friction surface is the inner surface of the ring and the yarn is pressed against the friction surface by means of a double or multi-stage lever arm. One disadvantage of this type of appliance is that there is a large increase in the running tension of the yarn as it passes through the unit. This is because it is necessary to urge the yarn into the cavity formed by the friction surface which is achieved by means of a yarn guide mounted on a lever arm but this requires a great change in the yarn direction to allow it to be forced against the friction surface and there is a large are of contact between the yarn and the guide which results in high friction and a large increase in yarn tension. A further disadvantage of this device is that the yarn can become constrained to move in such a direction thatits vector in the direction of travel of the friction surface is opposite to the direction of travel of the surface and this introduces an addi tional frictional force and thus a further increase in the tension in the yarn. In addition twists in a yarn do not readily pass over an obstacle in the yarn path and thus even if a high twist is generated between the rotating friction surface and the yarn guide it may not pass the yarn guide itself to run back to the heater and thus may only be used to produce false twist yarns of low twist. Thus this appliance does not achieve the desired effect of producing maximum twisting with minimal increase in tension. This increase in tension is particularly undesirable in the texturising of undrawn as opposed to drawn thermoplastic synthetic yarns, for instance nylon 6.6, nylon 6, polyester or polyacrylonitrile yarns, where drawing and bulking are carried out either in immediate succession or simultaneously. In these processes the tension in the yarn before it enters the friction unit is generally considerably greater than in processes where drawn yarn is twisted which means if twisting results in an increase in tension, there is a probability that the fibre will be damagedgWe have found that this also results in a higher yarn break rate.

According to the present invention we provide a device for imparting twist to a moving yarn comprising a rotatable friction surface together with a rotatable yarn guide element which holds the yarn against said friction surface and rotates as the yarn passes thereover. The present invention also provides a process for imparting twist to a moving yarn wherein the yarn is urged against a rotating friction surface by means of a yarn guide element around which the yarn is wrapped and which rotates as the yarn passes in contact with the guide element. y

We prefer that the yarn element rotates freely and independently of the friction surface as this gives good control of yarn tension. The axes of rotation of the yarn guide element and the friction surface can be identical. Any suitably shaped friction surface may be used in our invention although we prefer to use a surface which requires a minimum change in the direction of travel of the yarn consistent with attaining the necessary area of contact and contact pressure between the yarn and the friction surface to produce the required twist in the yarn. Our preferred friction surface therefore comprises an annular bush which is so shaped and mounted that the frictional contact between the yarn and the bush takes place outside the space defined by the annulus and the yarn is held against the friction surface by being wrapped around the rotatable yarn guide element which extends to within the volume defined by the annular bush. This has the added advantage that the top and outer surfaces of the yarn are moving faster than the inner surface and thus imparts a greater degree of twist than would be imparted by the inner surface. Thus in this embodiment the yarn approaches and leaves the bush from the same side with little increase in tension due to contact with the yarn guide element firstly because it is not necessary to impart a drastic change in yarn direction to ensure contact with the friction surface and secondly because the guide element rotates with the movement of the yarn.

Our preferred shape for the friction surface is an annulus whose normal cross section is flat or convex where it contacts the yarn so that the upper, i.e., outside and top surfaces of the friction ring impart the twist to the yarn. Thus the twisting is effected over the area of the ring where the normals to the ring surface are either parallel to or point away from the direction of the axis of rotation of the ring. Any contact between the yarn and the part of the surface whose normals point towards the axis of rotation is though only to stabilise the position of the yarn.

The friction element should preferably be mounted so that as the yarn is fed from the yarn source to the yarn guide element it is held against the upper surface of the ring. The shape of the upper surface and the angles through which the path of the yarn is forced to travel to obtain the contact with the friction surface may be adjusted as is necessary to achieve the required twist density whilst providing a control over yarn tension.

The preferred surface profile of the yarn guide element depends upon required twist density and tension in the yarn. The yarn guide element may be cylindrical, conical, concave or convex and the shape should be chosen to allow free travel of the yarn as it is wrapped around the guide element without slippage.

When using the preferred form of annular friction device described above we prefer that the yarn guide be tapered with the thinner part extending into the volume defined by the bush. The yarn guide element is preferably mounted so that it may rotate independently of the friction surface and may be mounted on roller bearings so that it is rotated by the travelling yarn which is wrapped around the guide element. In an alternative embodiment the yarn guide element may itself be driven and possibly at the same speed as the friction surface. In this instance the tension in the yarn may be controlled by careful choice of the effective diameter of the yarn guide element. Thus in the operation of our preferred embodiment the yarn first of all moves under tension over the friction surface and is wrapped around the freely rotatable yarn guide. The wrap may be in or against the direction of rotation of the friction surface. The yarn guide ensures contact with one or both friction surface parts as described above. With this device, a false twist can be produced in any yarns having a positive surface friction. The device can be used to particularly good advantage especially when false twisting drawn synthetic thermoplastic yarns, synthetic yarns drawn immediately beforehand in one operation and undrawn synthetic yarns, e.g., yarns from nylon 6, nylon 6;6, polyester etc. As described above false twisting is a process in which yarn is twisted so that the twist runs back along the yarn into a zone where it is heated and the twist set. In this technique the action of the twist bush is two fold in that it imparts a twist in the yarn that is being fed to the bush and detwists the yarn as it leaves the bush. The techniques of the present invention may readily be used in the twisting step of such a process. The tension before the friction unit during texturising and the tensions in undrawn yarn are as a rule considerably higher than the corresponding tensions during the texturising of drawn yarns, so that the smaller increase in tension when the yarn runs through the friction unit has a positive effect on the steadiness of running and is less likely to damage the yarn. In addition, the stringing-up of the yarn at the beginning of the process is particularly straightforward as the yarn may readily be wrapped around the yarn guide either by a suction gun, a mechanical device or by hand.

The present invention further provides an apparatus for imparting twist to moving yarn comprising an annular rotating friction surface urging the yarn against said friction surface and means for withdrawing the twisted yarn wherein the feeding and withdrawing means are positioned so that the yarn approaches and leaves the rotating friction surface on the same side and the means for urging the yarn against said friction surface comprises a rotatable member extending within the volume defined by the annular rotating friction surface so that when the moving yarn is wrapped around the member it is held against the friction surface.

The present invention is illustrated but in no way limited by reference to the accompanying drawings in which FIG. 1 illustrates an apparatus of the present invention FIG. 2 is a view taken in direction X of FIG. 1

FIG. 3 is an alternative apparatus according to the present invention FIG. 4 is a view taken in direction Y of FIG. 3

Referring now to FIG. 1 the apparatus consists of a spindle 1 mounted on a shaft 2, roller bearings 6 are provided between the shaft and the spindle to allow the spindle to be rotated on the shaft by belt 5. The friction ring 4 is mounted within the channel formed at the end of the spindle l and is shaped so that the outside and top surface 7 of the friction surface extends beyond the end of the spindle and then curves away to the inner ring defining surface 8.

The shaft 9 is an extension of the spindle 1 and the conical body 3 is mounted on the shaft by means of roller bearings 10 so that it does not rotate with the shaft 9. Thus in operation the yarn 1 1 passes over the friction surface 7 and around the conical guide member 3 which is free to rotate as the yarn passes round it by virtue of the roller bearings 10. FIG. 2 illustrates the yarn wrap round, the numerals representing the same features as in FIG. 1.

FIG. 3 illustrates another apparatus according to the present invention. The spindle and friction surface are identical in construction and operation with that of FIG. 1 but the yarn guide member is different. In this embodiment the yarn guide member is mounted entirely independently of the spindle and friction surface and consists of a conical member 12 mounted in the support 13 by means of roller bearings 14 in such a way that 12 is free to rotate about 13. The support 13 is itself mounted on an adjustable lever 15 which may be moved to and fro to facilitate strining-up of the yarn l6 and to increase or decrease the contact pressure between the yarn and the friction surface if this is necessary.

The yarn wrap in this apparatus is shown in FIG. 4 and the apparatus operates in a similar manner to the apparatus illustrated in FIG. 1.

The present invention is further illustrated by reference to the accompanying examples in which the tensions in the yarn were measured using a Schmidt tensometer.

EXAMPLE 1 Drawn nylon yarn was fed first over a feed roll then in close contact with a 1.50 meter long plate heater, then over guides through a l.0 meter long cooling zone to a false twist device of the type illustrated in FIG. 1 and finally through a second roll to a wind up. The twist applied by the false twisting device was imparted to the yarn and was present in the part of the yarn which was heated to the thermoplastic region. Detwisting occurred after the yarn had passed through the false twisting device.

EXAMPLE 2 Example 1 was repeated starting with undrawn nylon yarn which was drawn immediately before texturising. In this operation three feed rolls were used, the yarn drawn between the first and second rolls and twisted between the second and third rolls.

EXAMPLE 3 Example 2 was repeated using undrawn polyester yarn as starting material.

The results of Examples 1 to 3 are summarised in the following table Example .Yarn Tension in yarn Tension in yarn Type before it enters before it leaves (Drawn friction unit in friction unit in Denier) grams grams I Nylon 6.6 22 Dtex 30 10 2 Nylon 6.6 U Dtex 100 100 3 Polyester 167 Dtex 150 160 Thus it can readily be seen that there is only a small increase (and in some cases a decrease) in the tension in the yarn as it passes through the friction unit.

EXAMPLE 4 For the purpose of comparison Example 1 was repeated using a twisting device in which the yarn is urged against the inner surface of a friction ring by a fixed arm guide The tension in the yarn entering the friction unit was 6 grams whereas the tension in the yarn leaving the unit was 25 grams.

EXAMPLE Example 4 was repeated using undrawn yarn which was drawn immediately before passing into the twist unit, the final denier of the drawn yarn was 22 dtex. In this case the tension in the yarn entering the twist unit was 10 grams and whereas that in the yarn leaving the unit was 46 grams.

EXAMPLE 6 Example 5 was repeated except that the yarn was drawn and twisted simultaneously. The tension in the yarn entering the twist unit was grams whereas that in the yarn leaving the unit was 65 grams.

Similar comparative experiments with other denier nylon yarns and with polyester yarns gave similar results.

I claim:

1. A device for imparting twist to a moving yarn comprising an annular rotating friction surface and a rotatable yarn guide element which holds the yarn against said friction surface and rotates as the yarn passes in contact with said guide element, said annular friction surface and rotatable guide element being shaped and mounted so that the yarn approaches and leaves the device on the same side of the device and the frictional 1 contact between the yarn and the friction surface takes place outside the space defined by the annulus.

2. A device for imparting twist to a moving yarn comprising an annular rotating friction surface and a rotatable yarn guide element which holds the yarn against said friction surface and rotates as the yarn passes in contact with said guide element, said annular friction surface and rotatable guide element being shaped and mounted so that the yarn approaches and leaves the de vice on the same side of the device and the frictional contact between the yarn and the friction surface takes place outside the space defined by the annulus, said rotatable yarn guide element extending to within the volume defined by the annular friction surface.

3. A device according to claim 2 in which the friction surface is an annulus whose cross section is flat or convex where it contacts the yarn so that yarn twisting is effected over the area of the annulus where the normals to the ring surface are either parallel to, or point away from the direction of the axis of rotation of the ring.

4. A device according to claim 2 in which the yarn guide is tapered with the thinner part extending into the volume defined by the bush.

5. A device according to claim 2 in which the yarn guide is rotatable independently of the friction surface.

6. A device according to claim 2 in which the yarn guide is rotated by the motion of the yarn around the guide.

7. An apparatus for imparting twist to moving yarn comprising an annular rotating friction surface, means for feeding yarn to said friction surface means for urging the yarn against said friction surface and means for withdrawing the yarn from said friction surface wherein the feeding and withdrawing means are positioned so that the yarn approaches and leaves the rotating friction surface on the same side thereof and the means for urging the yarn against said friction surface comprises a rotatable means extending within the volume defined by the annular rotating friction surface so that when the moving yarn is wrapped around the member it is held against the friction surface.

8. An apparatus according to claim 7 containing a heater positioned to heat the yarn before it reaches the friction surface so that when the twist imparted to the yarn runs back along the yarn it is set by the heater.

9. A process for imparting twist to a moving yarn comprising the step of urging said yarn against an annular rotating friction surface at a point outside the space defined by the annulus by means of a yarn guide element around which the yarn is wrapped and which rotates as the yarn passes in contact therewith, said yarn guide element extending within the volume defined by the annulus, said yarn approaching and leaving the friction surface on the same side of said surface.

10. A process according to claim 9 in which the yarn guide element rotates freely and independently of the friction surface.

11. A process for the production of texturised yarn comprising heating yarn, twisting the yarn by a process according to claim 9 and allowing the twisted yarn to untwist.

12. A process according to claim 11 in which the yarn is drawn yarn and is continuously fed to the heater from a zone in which it has been drawn. 

1. A device for imparting twist to a moving yarn comprising an annular rotating friction surface and a rotatable yarn guide element which holds the yarn against said friction surface and rotates as the yarn passes in contact with said guide element, said annular friction surface and rotatable guide element being shaped and mounted so that the yarn approaches and leaves the device on the same side of the device and the frictional contact between the yarn and the friction surface takes place outside the space defined by the annulus.
 2. A device for imparting twist to a moving yarn comprising an annular rotating friction surface and a rotatable yarn guide element which holds the yarn against said friction surface and rotates as the yarn passes in contact with said guide element, said annular friction surface and rotatable guide element being shaped and mounted so that the yarn approaches and leaves the device on the same side of the device and the frictional contact between the yarn and the friction surface takes place outside the space defined by the annulus, said rotatable yarn guide element extending to within the volume defined by the annular friction surface.
 3. A device according to claim 2 in which the friction surface is an annulus whose cross section is flat or convex where it contacts the yarn so that yarn twisting is effected over the area of the annulus where the normals to the ring surface are either parallel to, or point away from the direction of the axis of rotation of the ring.
 4. A device according to claim 2 in which the yarn guide is tapered with the thinner part extending into the volume defined by the bush.
 5. A device according to claim 2 in which the yarn guide is rotatable independently of the friction surface.
 6. A device according to claim 2 in which the yarn guide is rotated by the motion of the yarn around the guide.
 7. An apparatus for imparting twist to moving yarn comprising an annular rotating friction surface, means for feeding yarn to said friction surface means for urging the yarn against said friction surface and means for withdrawing the yarn from said friction surface wherein the feeding and withdrawing means are positioned so that the yarn approaches and leaves the rotating friction surface on the same side thereof and the means for urging the yarn against said friction surface comprises a rotatable means extending within the volume defined by the annular rotating friction surface so that when the moving yarn is wrapped around the member it is held against the friction surface.
 8. An apparatus according to claim 7 containing a heater positioned to heat the yarn before it reacheS the friction surface so that when the twist imparted to the yarn runs back along the yarn it is set by the heater.
 9. A process for imparting twist to a moving yarn comprising the step of urging said yarn against an annular rotating friction surface at a point outside the space defined by the annulus by means of a yarn guide element around which the yarn is wrapped and which rotates as the yarn passes in contact therewith, said yarn guide element extending within the volume defined by the annulus, said yarn approaching and leaving the friction surface on the same side of said surface.
 10. A process according to claim 9 in which the yarn guide element rotates freely and independently of the friction surface.
 11. A process for the production of texturised yarn comprising heating yarn, twisting the yarn by a process according to claim 9 and allowing the twisted yarn to untwist.
 12. A process according to claim 11 in which the yarn is drawn yarn and is continuously fed to the heater from a zone in which it has been drawn. 